A ball valve is one of several types of “quarter-turn” closing valves. Such valves are usually held between two sealed connections and operate by the turning of a ball inside a valve body. The ball has a through hole or port that can be lined up with the open ends of the valve to permit flow. When the ball is turned, by an attached handle or other actuator, the port becomes smaller and blocks flow through the valve. Usually, if the ball is turned a full 90°, the port becomes perpendicular to the ends of the valve and blocks flow entirely. Variations can utilize a ball with more than one port, such that when the valve is turned, flow is redirected through a different valve and further turning can close off flow entirely. Larger valves with heavier balls, such as those used on pipelines or water mains may additionally use trunnions to help support the ball and prevent damage to internal components.
Ball valves are desirable for use in industry because they enable quick opening and a leak-proof closed seal. However, ball valves used in industrial applications are often exposed to various chemical compounds, liquid or gaseous, that can have a corrosive effect on the components, which can compromise the internal seals. It is not unusual for ball valves used in industry to be exposed to excessive temperatures (below 0° F. to over 1000° F.) and pressure (10−10 mm Hg to over 100 PSI). Most often, the seals between the central valve stem and the stem seal are the most vulnerable. A common implementation of stem seals to those skilled in the art is an o-ring. For the purposes of this discussion, the terms stem seal and o-ring are interchangeable.
Elevated temperatures are particularly problematic and can have the greatest effect because of expansion of the stem seal material. Various specialized metallic or elastomeric materials have been developed to withstand the chemical or environmental extremes for each application. Valve body designs have also been improved to accommodate for stem seal expansion within the valve gland. Nonetheless, extrusion of the stem seal material into surrounding spaces during temperature-induced expansion is still a problem. Further, it can have a deleterious effect not only on the integrity of the stem seal, but on the surrounding components with which the expanding stem seal material comes into contact.
As technology changes and develops, ball valves are increasingly utilized in a greater variety of industrial applications. As such, it is necessary for ball valve seals to withstand a multitude of conditions, including even greater temperature extremes and corrosive conditions. There is a need for a ball valve design capable of withstanding high temperature and high pressure conditions with minimal or no leakage. More particularly, there is a need for a ball valve design that can provide the necessary leakage control at different temperatures and accommodate for temperature- or chemical-induced expansion of stem seal materials.